1. Field of the Invention
The present invention relates to a strain gauge type semiconductor pressure detecting device for detecting relatively high pressure.
2. Description of the Related Art
A strain gauge type semiconductor pressure detecting device of the prior art is disclosed, for example, in Japanese Non-examined Patent Publication No. 7-294353. The semiconductor pressure detecting device disclosed in this publication has a pressure sensor chip 104 mounted in a recess 101b, formed in a body 101, via a metal base 102 (which corresponds to a base plate of the present invention) and a glass base 103, wherein pressure is introduced via through holes 101a, 102a, 103a made in the body 101, the metal base 102 and the glass base 103, respectively, to be concentric with each other, and is applied to the pressure sensor chip 104. While the metal base 102 is fixed by laser welding of the periphery thereof onto the body 101, a circular groove 102b concentric with the through hole 102a is formed inside the laser-welded portion in this prior art example, thereby making the central portion relatively raised so that the glass base 103 and the pressure sensor chip 104 are not subject to undesirable stress caused by thermal expansion of components due to the heat of laser welding.
However, the semiconductor pressure detecting device of the prior art has such a problem that since the laser welding step takes much time, the device can not produced at low cost. Use of the projection welding step may be conceived to counter this problem, but this causes another problem that impact generated during bonding or residual thermal stress may cause breakage in the joint of the base. Further, there has been such a problem that applying a high extraneous pressure causes the metal base to warp, and sufficient margin in the measurement range cannot be obtained for measuring high pressure.